With bagpipes and banners, anti-gay marriage protestors from the American Society for the Defense of Tradition, Family and Property stormed the Main Green yesterday.

Garbed in formal black and red attire and hoisting medieval-looking banners, a faction of the American Society for the Defense of Tradition, Family and Property — a national organization that opposes gay marriage — descended on the Main Green at approximately 11 a.m. yesterday.

The men were there to defend tradition, said John Ritchie, the group’s spokesman. “Homosexuality is a violation of God’s natural law,” he said. The Pennsylvania-based organization has over 200,000 members nationwide, 5,000 of whom reside in Rhode Island.

The group, which originally positioned itself in the middle of the Green, used bagpipes to attract the attention of more than 20 onlookers before being forced to relocate to public property by the Department of Public Safety.

The organization — currently on tour — is making a number of stops throughout Rhode Island, and leaders thought the University would be an important place to stage a protest, Ritchie said.

The protestors stayed on the Green for approximately 15 minutes before moving to the sidewalk behind the Stephen Roberts ’62 Campus Center, said Paul Shanley, deputy chief of DPS.

Shanley, who has been with the University for four years, said he has never seen anything like it. Most protests are associated with student groups, he said, but this group seemed “entirely independent.”

Three men held aloft a sign reading “God’s Marriage = 1 Man & 1 Woman” and a lopsided red banner emblazoned with a golden lion. According to multiple onlookers, an unidentified male intentionally ran into the sign early in the protest.

“I’m really offended,” said Kerry McKittrick ’13, one of the first students to see the protest on the Green. “It’s essentially a hate rally.”

Students opposing the group mobilized quickly, scrawling makeshift signs, hoisting a rainbow door and handing out rainbow pins to passersby. As classes let out at noon, numbers swelled into the hundreds, and curious onlookers pressed up against the windows of the four floors of J. Walter Wilson.

Aida Manduley ’11, Queer Alliance head chair and Queer Coordinating Committee leader, said she heard about the protest from a friend’s text message. She ran to her dorm to don a rainbow outfit, sent out Facebook and email messages “to rally the troops” and hurried to the Green.

The student response was “tremendous,” Manduley said.

“We know they have a right to free speech,” she said of the anti-gay marriage group. But if speech is hateful, “the Brown community will not stay silent,” she added.

When one of the group’s volunteers tried to give University Chaplain Janet Cooper Nelson a pamphlet, she said she handed it back to him and told him her position.”He just looked stunned,” she said. Cooper — who has worked to advance the issue of gay marriage in the state for “a long time” — did not wait for a response.

“If there had been any opportunity for real conversation, I would have tried to take it,” she added. “I didn’t think there was, and I just kept walking.”

“It’s really showing how gay-friendly Brown is,” said Charlie Greene ’13 of the student response to the protest.

Brynn Smith ’11 said she was going to work when she caught wind of the protest and rushed to help.

As a senior, Smith has seen protests of this sort before, but they have “never been so explicitly hateful, so explicitly tasteless,” she said.

Manduley said she thought the group came to the University to gain media attention for its cause. “Because it’s a college and there’s this idea that kids are wild and crazy, especially at Brown, they think they can find fodder for their anti-LGBTQ rhetoric,” she said.

The group has just come from Maryland, said full-time volunteer Danniel Pribble, where a bill to legalize gay marriage recently died in the state House of Representatives. They visited Warwick Tuesday and received many more supportive honks from drivers than at Brown, he said.

Only a few of the many cars fighting through the mass of students and protestors on Waterman Street honked in support of the group.

Cries of, “Hey ho, homophobia’s got to go” and “What do we want? Equality!” nearly drowned out the strains of patriotic music emanating from the group’s bagpipes and drums.

At one point during the protest, two female students kissed in front of the flag-bearers to raucous cheers from onlookers.

“We’re interested in a conversation,” said Benedict Landgren Mills MD’14, wrapped in a rainbow blanket. “But this is not the milieu for it.”

Shredded pamphlets littered the sidewalk as students crowded around volunteers to ask questions, shout obscenities and try to engage in conversation with them.

Sarah Engle ’11 pointed to the lack of meaningful evidence supporting the group’s assertions. Its literature, which lists 10 reasons “why homosexual ‘marriage’ is harmful and must be opposed,” cites no specific passages of scripture to support its claims, she said.

The group was woefully unprepared for the outspoken, activist nature of the University, Engle added. “If you’re going to come here, you need to bring some facts.”

“I’m reporting to Genesis,” Miller said in response to student accusations that the group failed to adequately support its claims.

The on-campus response to the protest was “middle of the road,” said John Miller, a full-time volunteer with the organization. Having been to many college campuses with the group, Miller expressed surprise at the nature of student arguments. “The intellectual level is below the Ivy League status,” he said.

At 12:20 p.m., the group packed up and led a military band-style march down Waterman, Thayer and George streets. Students and community members followed close behind, chanting “two, four, six, eight, get your hate out of our state!” Some tried to jump in front of the group to bring it to a halt, but they were admonished by DPS officers for blocking the public sidewalk.

“They were essentially leading a gay pride parade,” Michael Stumpf ’13 said of the ending march, adding that one of the volunteers he spoke with admitted that the group’s mission is sometimes counterproductive.

About an hour and a half after their initial arrival, the men rolled up their red banners, piled into three vans and drove off. Their departure, met with the enthusiastic cheers of about 150 onlookers, was set to the tune of a male student saxophonist playing the “Star-Spangled Banner.”

In the coming days, the LGBTQ community will decide how to officially reply to the protest, Manduley said. The LGBTQ Resource Center held office hours yesterday from 6 to 8 p.m. to offer students a chance to decompress after the day’s events.

For now, she said, “I felt like it was a really great thing to have happen at Brown because of how we chose to respond.”